Generally, electrostatic coating is a coating method of efficiently coating a coating target with a paint by use of an electrostatic force between the paint and the coating target. Here, the electrostatic force is caused to act by negatively charging paint particles and by forming an electrostatic field (lines of electric force) with application of a high voltage between the coating target as a grounding electrode and an electrode of a coating device side as a cathode. The electrostatic coating can produce effects such as improvement in coating efficiency (reduction in a coating time owing to improved wrap around), and improvement in transfer efficiency (reduction in an amount of paint used owing to an improved volume ratio of paint transferred on a coating target). Further, note that the wrap around indicates an effect of causing a paint applied from the front side of a coating target to wrap around the coating target and to be transferred onto the back side of the coating target.
Conventional electrostatic coating methods are classified, in accordance with a way of atomizing a paint, into three types, i.e., an air atomization method, an air-less atomization method, and a rotary atomization method (atomization with a bell or a disk). In addition, in accordance with the high-voltage application method for generating an electrostatic force, the conventional electrostatic coating methods are classified into a direct application method and a corona discharge method. The direct application method is applied only to the rotary atomization method, and the corona discharge method is mainly applied to the air atomization method and the air-less atomization method. Also, note that, as one type of the corona discharge method, there is an external charging method in which a corona discharge electrode and a paint spray unit are disposed separated from each other, and a paint is electrostatically charged in a space before reaching a coating target. This method is mainly used for a highly-conductive paint (such as an aqueous paint) through which the high voltage leaks from a paint route if a general method is used in which the corona discharge electrode is disposed in the paint spray unit.
The conventional electrostatic coating techniques are composed by a combination of the paint atomization methods and the high-voltage application methods, but use a common electrostatic coating mechanism. Specifically, in any combination, an electrostatic force is caused to act in such a way that paint particles are electrostatically charged to fly along an electrostatic field formed between a coating machine (actually, a corona discharge electrode or a rotary atomizing head) and a coating target.